The present invention relates to apparatus and methods for processing substrates such as semiconductor substrates for use in IC fabrication or glass panels for use in flat panel display applications. More particularly, the present invention relates to controlling a plasma inside a plasma process chamber.
Plasma processing systems have been around for some time. Over the years, plasma processing systems utilizing inductively coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, and the like, have been introduced and employed to various degrees to process semiconductor substrates and glass panels.
During processing, multiple deposition and/or etching steps are typically employed. During deposition, materials are deposited onto a substrate surface (such as the surface of a glass panel or a wafer). For example, deposited layers such as SiO2 may be formed on the surface of the substrate. Conversely, etching may be employed to selectively remove materials from predefined areas on the substrate surface. For example, etched features such as vias, contacts, or trenches may be formed in the layers of the substrate.
One particular method of plasma processing uses an inductive source to generate the plasma. FIG. 1 illustrates a prior art inductive plasma processing reactor 100 that is used for plasma processing. A typical inductive plasma processing reactor includes a chamber 102 with an antenna or inductive coil 104 disposed above a dielectric window 106. Typically, antenna 104 is operatively coupled to a first RF power source 108. Furthermore, a gas port 110 is provided within chamber 102 that is arranged for releasing gaseous source materials, e.g., the etchant source gases, into the RF-induced plasma region between dielectric window 106 and a substrate 112. Substrate 112 is introduced into chamber 102 and disposed on a chuck 114, which generally acts as a bottom electrode and is operatively coupled to a second RF power source 116. Gases can then be exhausted through an exhaust port 122 at the bottom of chamber 102.
In order to create a plasma, a process gas is input into chamber 102 through gas port 110. Power is then supplied to inductive coil 104 using first RF power source 108. The supplied RF energy passes through dielectric window 106 and a large electric field is induced inside chamber 102. The electric field accelerates the small number of electrons present inside the chamber causing them to collide with the gas molecules of the process gas. These collisions result in ionization and initiation of a discharge or plasma 118. As is well known in the art, the neutral gas molecules of the process gas when subjected to these strong electric fields lose electrons, and leave behind positively charged ions. As a result, positively charged ions, negatively charged electrons, and neutral gas molecules (and/or atoms) are contained inside the plasma 118.
Once the plasma has been formed, neutral gas molecules inside the plasma tend to be directed towards the surface of the substrate. By way of example, one of the mechanisms contributing to the presence of the neutral gas molecules at the substrate may be diffusion (i.e., the random movement of molecules inside the chamber). Thus, a layer of neutral species (e.g., neutral gas molecules) may typically be found along the surface of substrate 112. Correspondingly, when bottom electrode 114 is powered, ions tend to accelerate towards the substrate where they, in combination with neutral species, activate the etching reaction.
Plasma 118 predominantly stays in the upper region of the chamber (e.g., active region), however, portions of the plasma tend to fill the entire chamber. The plasma typically goes where it can be sustained, which is almost everywhere in the chamber. By way of example, the plasma may contact areas on the chamber wall 120 and elsewhere if there are nodes in the magnetic field(s) confining the plasma. The plasma may also be in contact with regions where plasma is not required for meeting process objectives (e.g., regions 123 below the substrate 112 and gas exhaust port 122 non-active regions).
If the plasma reaches non-active regions of the chamber wall, etch, deposition, and/or corrosion of the areas may ensue, which may lead to particle contamination inside the process chamber, i.e., by etching the area or flaking of deposited material. Accordingly, the chamber may have to be cleaned at various times during processing to prevent excessive build-ups of deposits (for example, resulting from polymer deposition on the chamber wall) and etched by-products. Cleaning disadvantageously lowers substrate throughput, and typically adds costs due to loss of production. Moreover, the lifetime of the chamber parts is typically reduced.
Additionally, plasma interaction with the chamber wall can lead to recombination of the ions in the plasma with the wall and thus a reduction in the density of the plasma in the chamber during processing. In systems using a larger gap between the substrate and the RF source, even greater plasma interaction and hence particle losses to the wall occur. To compensate for these increased losses, more power density is needed to ignite and maintain the plasma. Such increased power leads to higher electron temperatures in the plasma and, consequently, leads to potential damage of the substrate and the chamber wall as well.
Finally, in chambers using non-symmetric pumping of source gases, better control of a magnetic plasma confinement arrangement can help shape the plasma and compensate for such non-symmetric pumping.
In view of the foregoing, there are desired improved techniques and apparatuses for controlling a plasma inside a process chamber.